When people find themselves in emergency conditions where immediate assistance is required, they may be out of touch or unable to get in touch with any assisting authority. Such emergency situations can arise both in military and civilian life and present a need for a personal identification beacon that can signal the proper authorities as to the location of the distressed person.
It is possible that the emergency situation may render the wearer of the beacon helpless or otherwise unable to activate his or her beacon. For example, such emergency situations may involve contact between the wearer of the beacon and hostile forces. Such conditions would require the beacon to signal for help in a way that is invisible to the hostile forces. For the beacon to be practical, it must be cost-efficient as well as small and portable.
In the past, mobile infrared (IR) units have been used to identify targets having one or more sources of infrared radiation. These IR units must operate independently of other radiation emissive sources, especially when used for targeting or surveillance purposes. In addition, such IR units must operate independently of a central network, as IR surveillance and identification is generally done by mobile independent field units. Examples of such prior art units are described in the patents mentioned below.
U.S. Pat. No. 5,396,243 describes an infrared laser battlefield identification beacon to be used in conjunction with forward looking infrared (FLIR) systems. A target vehicle's beacon system is triggered by a secure radio transmission from an approaching attack vehicle. The beacon uses an infrared source, which is a CO.sub.2 laser that initiates two or more infrared pulses, which the attacking vehicle would then detect.
U.S. Pat. No. 5,001,488 describes an identification friend or foe (IFF) method and system wherein an IFF interrogator, having its transmission antenna joined to an infrared camera, transmits a coded radar signal to a potential target vehicle. Friendly vehicles are equipped with an IFF receiver and an infrared laser response, which is then read by the interrogator. The transducer of the detecting vehicle is directional, such that its receiving lobe must be pointed towards each station to be interrogated.
U.S. Pat. No. 5,299,227 describes a beacon identification system which enables distinction between friend or foe. The invention consists of a beacon and a special purpose detector. The beacon continuously transmits pulse-coded infrared radiation, maintaining a covert signal through selection of the optical wavelength used by the beacon and through the use of a spread spectrum output signal. The beacon's signal would not be visible to those using existing night vision equipment because a specially designed detector must be used to detect the beacon's signal.
U.S. Pat. No. 4,763,361 describes a system and device for vehicle recognition or IFF use, wherein an unpolarized light source, such as an infrared laser or short wavelength radar, is used to interrogate a potential target. On a friendly vehicle, a wire grid polarizer is mounted to vary the polarization of the interrogation signal. A corner reflector, mounted to the back of the grid polarizer, utilizes the principle of optical enhancement to return an interrogation signal that has been collimated and diffraction limited. A wire grid polarization analyzer is mounted rotatively on the front of a detector to receive the signals reflected from the potential target.
U.S. Pat. No. 5,130,713 describes an IFF system that includes an interrogation device which cooperates with an answering device. The interrogation device operates in the high frequency (HF) or microwave range and has relatively broad radiation characteristic for transmitted HF interrogation pulses and for receiving HF answer signals. A pulse laser operating in the optical range is used as a position finding device and the answer signal is only triggered when the transmitted pulse of the laser transmitter arrives during an HF interrogation pulse produced by the interrogation transmitter.
U.S. Pat. No. 4,975,705 describes a target detector provided with transmitter means for simultaneously generating laser and radar waves. The target detector is also provided with receiving means for obtaining target signals comprising target information received by reflected laser and/or radar waves, and also by passive infrared emissions.
The disadvantages of such prior art mobile IR units include the units' unavailability as a distress beacon for an individual. For example, such IR units have considerable power demands, as well as large housing requirements, that would make the unit cumbersome to use and transport by an individual user. In addition, because of their complexity, these IR units require specialized knowledge for their operation, thereby precluding their availability to the general population. Furthermore, such prior IR units are costly and are not on a centralized network system of the type available to an assisting authority, such as the local police.